Files of the form date_time_AR_magnetic_environ.fits contain the excess magnetic energy density rho_e 
(Leka & Barnes 2003, ApJ, 595, 1277) and a measure for identifying strong-gradient polarity inversion 
lines r (Schrijver 2007, ApJL, 655, L117, doi: 10.1086/511857):

The first (primary) HDU is an (nx,ny) dimensional array containing the two-hour averaged rho_e. 
WCS information is provided in the headers to construct the coordinates of each pixel:
xn_i = CRVALn + CDELTn * (i - CRPIXn)
The analysis time interval used to calculate the mean is given by the keywords T_START and T_STOP.

The second (first extension) HDU is an (nx,ny) dimensional array containing the two-hour averaged r. 
WCS information is provided in the headers to construct the coordinates of each pixel:
xn_i = CRVALn + CDELTn * (i - CRPIXn)
The analysis time interval used to calculate the mean is given by the keywords T_START and T_STOP.
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Example code in IDL to read in both parameters:

data=readfits(path+'2011-09-07T01:12:00_AR11283_magnetic_environ.fits', header, ext=0) ; to read in rho_e

data=readfits(path+'2011-09-07T01:12:00_AR11283_magnetic_environ.fits', header, ext=1) ; to read in r

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Example header:

XTENSION        STRING    'IMAGE'
   SIMPLE          INT              1
   BITPIX          LONG               -64
   CONTENT         STRING    'Schrijver R density'
   NAXIS           LONG                 2
   NAXIS1          LONG               922
   NAXIS2          LONG               520
   T_REC           STRING    '2011.09.07_01:12:00'
   NTIMES          LONG                 2
   T_START         STRING    '2010.10.16_00:24'
   T_STOP          STRING    '2010.10.16_02:12'
   HARPNUM         STRING    '833'
   NOAA_AR         LONG             11283
   NOAA_NUM        LONG                 1
   NOAA_ARS        STRING    '11283'
   TELESCOP        STRING    'SDO/HMI'
   CTYPE1          STRING    'HPLN-TAN'
   CTYPE2          STRING    'HPLT-TAN'
   CDELT1          DOUBLE          0.50430700
   CDELT2          DOUBLE          0.50430700
   CUNIT1          STRING    'arcsec'
   CUNIT2          STRING    'arcsec'
   CRPIX1          DOUBLE           56.742200                            
   CRPIX2          DOUBLE          -82.869100
   CRVAL1          DOUBLE           0.0000000
   CRVAL2          DOUBLE           0.0000000
   CROTA2          DOUBLE         0.082595800
   RSUN_OBS        DOUBLE           952.11300
   RSUN_REF        DOUBLE       6.9600000e+08
   XCEN            DOUBLE           380.11990
   YCEN            DOUBLE          -418.14471
   PCOUNT          LONG                 0
   GCOUNT          LONG                 1
   COMMENT         STRING    Array[5]
   HISTORY         STRING    Array[5]
   
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